Removal of aluminum from a zeolite framework was first reported in 1964 by Barrer and Makki. They extracted aluminum from clinoptilolite by refluxing with hydrochloric acid. Depending on the acid concentration, up to 100% of the framework aluminum could be removed; however, the thermostability of the products gradually decreased at dealumination degrees higher than 65%. Dealumination with acids was accompanied by ion exchange of lattice cations by protons. The overall process was suggested to proceed according to Eq. (1) under formation of defect sites later generally denoted by the term “hydroxyl nest”